Tire-forming drum and method of manufacturing a green tire

Abstract: A tire-forming drum (10) is arranged such that first tapered portions (14E) of segments (14A, 14B) constituting each of a pair of side drums (14) and second tapered portions (12E, 12F) of segments (12A, 12B) constituting a center drum (12) are adapted to slide with respect to each other. As the segments of the center drum (12) are pressed by the segments of the side drums (14) from inside in a radially outward direction, the segments of the center drum (12) move radially outwardly, and the side drums (14) enter to the radially inner side of the center drum (12). Consequently, a green tire of an up-down structure can be formed by a single tire-forming drum, so that a green tire excelling in uniformity can be manufactured by a single-stage method.

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a tire-forming drum, and more particularly to a tire-forming drum and a method of manufacturing a green tire which make it possible to efficiently form a tire excelling in uniformity. Description of the Related Art: As methods of manufacturing a green tire, a single-stage method and a two-stage method are employed, and the formation of a carcass ply of an up-down structure has been possible only by the two-stage method, and has been impossible by the single-stage method. In the single-stage method, after a carcass ply 202 is attached to a center bladder 200 and a bead core 204 is set as shown in Fig. 8A, the center bladder 200 is inflated with air, and a side bladder 206 is also inflated so as to turn up a ply end portion inwardly in such a manner as to wrap the bead core 204, thereby obtaining a green case. When an attempt is made to form a tire of the up-down structure by the single-stage method, it is necessary to attach a down-ply to an up-ply (corresponding to the carcass ply 202 in Figs. 8A and 8B) after the up-ply is attached. However, since the up-ply which is supported by the inflated center bladder is liable to be deformed by an external force (since the center bladder inflated with air is soft), it is difficult to maintain a proper shape and attach the down-ply in a fixed shape. For this reason, the formation of a tire adopting the up-down structure could not be coped with by the single-stage method which is considered to be desirable in ensuring the uniformity of the tire. However, in the two-stage method, although it is possible to form a tire of the up-down structure, it is necessary to effect an operation in which after a hollow cylindrical carcass is formed by a carcass former, the carcass is removed from the carcass former and transferred onto a shaping former. Hence, there are cases where the carcass is undesirably deformed during the transfer and mounting thereof onto the shaping former, constituting a bottleneck in improvement of the uniformity of the tire. In the single-stage method, although the transferring operation is not required unlike the two-stage method, and there is no risk of deformation of the green case, it is impossible to form a tire of the up-down structure, as described above. In the two-stage method, on the other hand, although it is possible to form a tire of the up-down structure, it is impossible to efficiently form a tire excelling in uniformity. FR-R-1 366 516, EP-A0 432 993 and DE-B-1 579 231 reveal, respectively, a tire-forming drum comprising: a center drum divided into a plurality of segments in a circumferential direction and capable of expanding or contracting in a radial direction; a pair of side drums respectively provided in juxtaposition to both axial sides of said center drum and each divided into a plurality of segments in the circumferential direction, said pair of side drums being capable of expanding or contracting in the radial direction and capable of being inserted into a radially inner side of said center drum; supporting means disposed coaxially with axes of said center drum and said side drums so as to support said center drum; urging means for urging said plurality of segments of said center drum in a direction in which a diameter of said center drum is reduced in the radial direction; a pair of slide bases for respectively supporting said pair of side drums in such a manner that said side drums are movable along an axial direction of said supporting means; side-drum-diameter enlarging means provided for each of said slide bases so as to enlarge and reduce a diameter of each of said side drums in the radial direction by moving said segments of each of said side drums in the radial direction; slide-base moving means for moving said slide bases along the axial direction of said supporting means; a center bladder formed in a hollow cylindrical shape in such a manner as to cover outer peripheral surfaces of said center drum and said side drums and to be inflatable radially outwardly of said center drum from a state in which said center bladder is adhered to the outer peripheral surfaces of said center drum and said side drums, both axial sides of said center bladder being respectively supported by said slide bases; a pair of bead-core fixing means respectively disposed on said slide bases and located on respective axial sides of said center bladder, said pair of bead-core fixing means being capable of expanding or contracting for supporting a pair of bead cores thereon in a radially outward direction of said bead-core fixing means; and a pair of side bladders respectively provided for said pair of slide bases and capable of expanding or contracting in the radial direction for turning up those end portions of an up-ply that project axially outwardly of the respective bead cores, from an axially outer side toward an axially inner side of said bead-core fixing means, said up-ply being attached to an outer peripheral surface of said center bladder. With the aforementioned tire-forming drum of FR-R-1 366 516, EP-A0 432 993 and DE-B-1 579 231 a single-stage method of manufacturing a green tire having an up-structure is carried out. In this single-stage method, a carcass ply serving as an up-ply is attached to the center bladder and the bead cores are positioned onto the carcass ply. Then the center bladder and/or the side bladders are inflated so as to turn up the up-ply end portions inwardly and wrap them around the bead cores, thereby obtaining the green carcass having an up-structure. SUMMARY OF THE INVENTION In view of the above-described circumstances, it is an object of the present invention is to provide a tire-forming drum and a method of manufacturing a green tire which make it possible to efficiently form a tire of an up-down structure excelling in uniformity. In accordance with a first aspect of the present invention, there is provided a tire-forming drum comprising the features of claim 1. In accordance with a second aspect of the present invention, there is provided a method of manufacturing a green tire, comprising: the features of claim 14. By using the tire-forming drum in accordance with the first aspect of the present invention, a tire of an up-down structure excelling in uniformity can be formed as follows: (1) The side drums are positioned in advance in juxtaposition to the axially opposite sides of the center drum. The outside diameters of the side drums are made in advance to conform to the outside diameter of the center drum by reducing the diameters of the side drums. In addition, the outside diameter of each bead-core fixing means is reduced in advance by a predetermined dimension in such a way as to be smaller than the inside diameter of the bead core. (2) The first carcass ply serving as an up-ply is attached to the center bladder. Positions of both ends of the first carcass ply are each set to be spaced apart a predetermined distance axially outwardly of the bead-core fixing means (i.e., on the side of the bead-core fixing means that is away from the center bladder). (3) Each annular bead core is inserted in such a manner as to be placed over the outer periphery of the first carcass ply, so as to be positioned over the radially outer surface of the bead-core fixing means. (4) The diameter of each bead-core fixing means is enlarged to fix each bead core together with the first carcass ply from inside. (5) Each bead filler is attached to the fixed bead core at a predetermined position thereof. (6) The two slide bases are moved toward the center drum by the slide-base moving means, thereby causing the first tapered portions of the segments constituting each side drum and the second tapered portions of the segments constituting the center drum to abut against each other. Subsequently, the side-drum-diameter enlarging means is operated to enlarge the diameter of each side drum by a small amount. Since the first tapered portions and the second tapered portions in contact with each other, the segments of the center drum are pressed by the segments of the side drums from inside in the radially outward direction, and are thereby moved in the radially outward direction. Consequently, both the diameters of the side drums and the center drum are enlarged. (7) The side bladders are inflated to turn up the axial end portions of the first carcass ply about the respective bead cores toward the axially inner side of the bead-core fixing means. (8) Each turn-up portion of the first carcass ply is pressed against and adhered to the main-body portion of the first carcass ply, the bead core, and the bead filler by using known stitching rollers or the like. At this juncture, since the side drums are disposed on the radially inner side of the first carcass ply, the turn-up portion can be reliably adhered to the main-body portion of the first carcass ply, the bead core, and the bead filler by being pressed by the stitching rollers. (9) The second carcass ply serving as a down-ply is attached to the first carcass ply serving as the up-ply. (10) The overall second carcass ply is pressed against and adhered to the first carcass ply by using known stitching rollers or the like. At this juncture, since the center drum and the side drums are disposed on the radially inner side of the second carcass ply serving as the down-ply, the second carcass ply can be reliably adhered to the first carcass ply by being pressed by the stitching rollers. (11) Each side tread is attached to the second carcass ply at a predetermined position thereof. (12) Each side tread is pressed against and adhered to the second carcass ply by using known stitching rollers or the like. Since the center drum and the side drums are disposed on the radially inner side of the second carcass ply as described above, the side tread can be reliably adhered to the second carcass ply by being pressed by the stitching rollers. (13) The center bladder is inflated by a predetermined amount to inflate the first and second carcass plies. At the same time, the slide bases are moved further in the axially inward direction (i.e., toward the center drum) by means of the slide-base moving means. At this juncture, the first tapered portions of the segments constituting each side drum and the second tapered portions of the segments constituting the center drum are slid with respect to each other. Consequently, the segments of the center drum are pressed and moved by the segments of the side drums from inside in the radially outward direction, and the side drums enter the radially inner side of the center drum. Hence, the bead cores are made to approach each other, thereby reducing the width between the bead cores. (14) Finally, additional component parts of the tire such as a belt and a top tread are attached at a predetermined position on the inflated carcass, thereby completing a green tire. By using the tire-forming drum of the present invention, the formation of a green tire of the up-down structure can be effected up to the completion thereof by a single tire-forming drum, and a green tire excelling in uniformity can be manufactured by the single-stage method. In addition, in accordance with the method of manufacturing a green tire in the second aspect of the invention, in the first step, the side drums are positioned in juxtaposition to the axial sides of the center drum, and the outside diameters of the center drum and the side drums are set to a substantially identical outside diameter. Then, the first carcass ply serving as the up-ply is attached to an outer periphery of the center bladder kept in close contact with outer peripheral surfaces of the center drum and the side drums, such that each axial end of the first carcass ply is located at a position spaced apart a predetermined distance axially outwardly of the bead-core fixing means. In the second step, each of the annular bead cores is placed over the radially outer surface of each of the bead-core fixing means via the first carcass ply attached to the center bladder. Then, the diameter of each of the bead-core fixing means is enlarged so as to fix each of the bead cores together with the first carcass ply from the inner side thereof in the radially outward direction. In the third step, a bead filler is attached to each fixed bead core at a predetermined position thereof. In the fourth step the pair of bead core fixing means is moved inwardly in said axial direction such that the distance between the pair of bead cores is shortened to a first predetermined distance; In the fifth step, the diameters of the side drums and the center drum are enlarged until the outer peripheral surfaces of the side drums and the center drum abut against an inner peripheral surface of the first carcass ply. In the sixth step, each axial end portion of the first carcass ply is turned up in an axially inward direction of the bead-core fixing means about the bead core with the bead filler attached thereto by inflating each of the side bladders, so as to cause each turn-up portion of the first carcass ply to be pressed against and adhered to a main-body portion of the first carcass ply, the bead core, and the bead filler. Hence, the positions of the bead cores are prevented from becoming offset during the turning-up operation in the fifth step. In addition, since the side drums are disposed on the radially inner side of the first carcass ply, the turn-up portion can be reliably adhered to the main-body portion of the first carcass ply, the bead core, and the bead filler by being pressed by known stitching rollers or the like. In the seventh step, the second carcass ply serving as the down-ply is attached to the first carcass ply whose axial end portions are turned up, so as to cause the entire second carcass ply to be pressed against and adhered to the first carcass ply whose end portions are turned up. Since the center drum and the side drums are disposed on the radially inner side of the second carcass ply, the second carcass ply can be reliably adhered to the first carcass ply by being pressed by known stitching rollers or the like. In the eighth step, each side tread is attached at a predetermined position on an outer peripheral surface of the second carcass ply adhered to the first carcass ply. In the nineth step, the center bladder is inflated so as to inflate the first carcass ply and the second carcass ply which are superposed on the center bladder. At the same time, the side drums and the pair of bead core fixing means are moved in respectively axially inward directions such that the distance between the pair of bead cores is shortened to a second predetermined distance, said second predetermined distance being shorter than the first predetermined distance, and at least one of the center drum and the side drums is expanded or contracted, and the side drums are inserted into the radially inner side of the center drum, so as to allow the bead cores to approach each other. In the tenth step, a belt and a top tread are attached at a predetermined position on the inflated second carcass ply superposed on the inflated first carcass ply. A green tire is manufactured through the above-described steps. Thus, in accordance with the method of the present invention for manufacturing a green tire, the formation of a green tire can be effected by a single tire-forming drum up to the completion thereof. Since the first carcass ply serving as the up-ply and the second carcass ply serving as the down-ply can be reliably adhered to each other, and the positions of the bead cores are prevented from becoming offset, green tires excelling in uniformity can be manufactured efficiently. The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view taken along the axis of a tire-forming drum in accordance with an embodiment of the present invention; Fig. 2 is a cross-sectional view taken along the axis of the tire-forming drum and illustrates a state in which a carcass ply for up-ply use is attached, and a bead core is fixed; Fig. 3 is a cross-sectional view taken along the axis of the tire-forming drum and illustrates a state in which a carcass ply for down-ply use and side treads are attached to the carcass ply for up-ply use after an end portion is turned up; Fig. 4 is a cross-sectional view taken along the axis of the tire-forming drum and illustrates a state in which the carcass is inflated; Fig. 5 is a cross-sectional view of the tire-forming drum taken along the line 5 - 5 of Fig. 1; Fig. 6 is a cross-sectional view of the tire-forming drum taken along the line 6 - 6 of Fig. 1; Fig. 7 is a radial cross-sectional view of a center drum in a state in which the diameter is enlarged; Fig. 8A is a cross-sectional view taken along the axis of a tire-forming drum used in a conventional single-stage method; and Fig. 8B is a cross-sectional view taken along the axis of the tire-forming drum shown in Fig. 8A, and illustrates a state in which the carcass mounted on the tire-forming drum is inflated, and an end portion is turned up. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to Figs. 1 to 7, a description will be given of an embodiment of a tire-forming drum in accordance with the present invention. As shown in Fig. 1, a tire-forming drum 10 is comprised of a center drum 12 and a pair of side drums 14 disposed on axially opposite sides of the center drum 12, respectively. It should be noted that, in the description of this embodiment, since the pair of side drums 14 are provided symmetrically with respect to the center drum 12, a description will be given of only one side drum 14. As shown in Fig. 5, the center drum 12 is divided into a plurality of segments in the circumferential direction. Specifically, large segments 12A, each having a radial cross section of a substantially arcuate shape and a larger circumferential dimension, and small segments 12B, each having a smaller circumferential dimension, are formed by being arranged alternately. In addition, as shown in Fig. 6, the side drum 14 is also divided into a plurality of segments in the same way as the center drum 12, and large segments 14A and small segments 14B each having a radial cross section of a substantially arcuate shape are formed by being arranged alternately. As shown in Figs. 5 and 6, each small segment 12B of the center drum 12 and each small segment 14B of the side drum 14 are provided with tapered surfaces 12D, 14D formed at circumferential end portions thereof on the outer peripheral side. Meanwhile, each large segment 12A of the center drum 12 and each large segment 14A of the side drum 14 are provided with tapered surfaces 12C, 14C formed at circumferential end portions thereof on the inner peripheral side. As shown in Fig. 1, a drive shaft 16, which constitutes a part of a slide-base moving means that is rotated by an unillustrated motor, is passed through axial portions of the center drum 12 and the side drum 14. A right-handed thread 18 and a left-handed thread 20 are respectively formed on opposite sides of the drive shaft 16 with a longitudinally central portion placed therebetween. A pipe 22 serving as a supporting means is disposed coaxially with the drive shaft 16 on the radially outer side thereof. This pipe 22 is supported by columns provided uprightly on an unillustrated floor. As shown in Figs. 1 and 5, a plurality of hollow cylinders 24 are provided radially around an outer periphery of the pipe 22 at a longitudinally central portion of the pipe 22. The diameter of the bore at a distal end of the hollow cylinder 24 is reduced, and a slide shaft 26 is slidably inserted into the hollow cylinder 24. A coil spring 28 serving as an urging means is disposed in the hollow cylinder 24, and the coil spring 28 abuts against a washer 30 secured to a radially inner end of the slide shaft 26, so as to urge the slide shaft 26 toward the drive shaft 16. The center segments 12A and 12B are each affixed to a distal end of the slide shaft 26 projecting from the hollow cylinder 24. It should be noted that the urging means is not limited to the coil spring 28, and any urging means may be used insofar as it is capable of urging the slide shaft 26 toward the drive shaft 16. As shown in Fig. 1, a pair of cylindrical slide bases 32 for supporting the respective side drums 14 are provided on the outer periphery of the pipe 22 on axially opposite sides of the center drum 12. The slide bases 32 are movable along the axial direction of the pipe 22. A pair of elongated holes 34 are formed in the pipe 22 in such a manner as to extend in the longitudinal direction of the pipe 22. A portion of each of two internally threaded members 36, which respectively mesh with the right-handed thread 18 and the left-handed thread 20 of the drive shaft 16 and constitute the other parts of the slide-base moving means, is passed through the elongated hole 34 and is coupled to the slide base 32. Accordingly, as the drive shaft 16 rotates, the slide bases 32 are capable of moving toward and away from each other. The slide base 32 is provided with a first cylinder hole 38 on the drive shaft 16 side. The first cylinder hole 38 is provided around the drive shaft 16 coaxially therewith, and has a radial cross section which is annular in shape. A plurality of rectangular holes 40 extending in the radial direction of the drive shaft 16 are provided circumferentially at predetermined pitches on that side of the first cylinder hole 38 that is located on the center drum 12 side. These rectangular holes 40 communicate with the first cylinder hole 38. An annular partition wall 42 is provided in an axially intermediate portion of the first cylinder hole 38 so as to divide the first cylinder hole 38 axially into two parts. In the first cylinder hole 38, an annular first piston 44 is disposed on the center drum 12 side of the partition wall 42, while an annular second piston 46 is disposed on the opposite side thereof. The first piston 44 and the second piston 46 are connected to each other by means of connecting shafts 50 inserted in through holes provided in the partition wall 42. It should be noted that O-rings (not shown) for maintaining airtightness are provided in axially intermediate portions of the through holes 48 in the partition wall 42 and on respective inner and outer peripheries of the first piston 44 and the second piston 46. Slide blocks 52 are disposed in the rectangular holes 40, respectively. The slide blocks 52 are movable in the rectangular holes 40 along the radial direction of the drive shaft 16. Each of the slide blocks 52 is formed as a hollow, box-shaped body, and one side of a link 54 is inserted into a hollow portion thereof. One end of the link 54 is swingably supported by a shaft 56 attached to a substantially central portion of the slide block 52, and the other end of the link 54 is swingably supported by a shaft 58 attached to an end of the first piston 44. For this reason, when the first piston 44 moves toward the center drum 12, the slide block 52 moves radially outwardly in the rectangular hole 40. When the first piston 44 moves away from the center drum 12, the slide block 52 moves radially inwardly in the rectangular hole 40. The large segment 14A or the small segment 14B of the side drum 14 is attached to a radially outer end of each slide block 52. It should be noted the first piston 44, the connecting shafts 50, the second piston 46, the links 54, the slide blocks 52, and the like constitute a side-drum-diameter enlarging means. The slide base 32 is provided with a second cylinder hole 60 on the radially outer side of the first cylinder hole 38. In the same way as the first cylinder hole 38, this second cylinder hole 60 is provided around the drive shaft 16 coaxially therewith, and has a radial cross section which is annular in shape. An annular piston 62 constituting a part of the bead-core fixing means is disposed in the second cylinder hole 60. This piston 62 is movable in the second cylinder hole 60 along the axial direction, and O-rings (not shown) for maintaining airtightness are provided on an axially intermediate portion of the piston 62 on inner and outer peripheries thereof. The piston 62 has a tapered surface 62A formed on its outer periphery on the center drum side. In addition, a plurality of rectangular holes 64 extending in the radial direction of the drive shaft 16 are provided circumferentially at predetermined pitches on that side of the second cylinder hole 60 that is located on the center drum 12 side. These rectangular holes 64 communicate with the second cylinder hole 60. A small slide block 66 constituting another part of the bead-core fixing means is disposed in each rectangular hole 64. The small slide block 66 is movable in the rectangular hole 64 along the radial direction of the drive shaft 16. A bead-placing portion 68 is formed on each small slide block 66 on the radially outer side thereof. The bead-placing portion 68 has an axial cross section of a substantially concave shape. The respective small slide blocks 66 are connected to each other by means of an annular resilient band, and are thereby urged toward the drive shaft 16. A friction-reducing roller 70, which is adapted to roll by abutting against the tapered surface 62A of the piston 62, is provided on the drive shaft side of the small slide block 66. A side bladder 72 is disposed on the outer peripheral side of the slide base 32. The configuration of the side bladder 72, when inflated with air, is shaped substantially like a doughnut, and is installed with its axially opposite ends fitted into grooves provided in outer peripheral portions of the slide base 32. As shown in Fig. 1, the side bladder 72, when not inflated with air, has its radially inner surface kept in close contact with the outer peripheral surface of the slide base 32, and its center drum-side end portion is mounted on the bead-placing portions 68. The slide base 32 is provided with the following pipelines: a pipeline 74 for inflating the interior of the side bladder 72 with air; a pipeline 78 for allowing air to move into or out of an air chamber 76 located between the second piston 46 and the partition wall 42; a pipeline 79 for allowing air to move into or out of an air chamber 77 located between the bottom of the second cylinder hole 60 and the piston 62; and a pipeline 82 for allowing air to move into or out of a second air chamber 80 located between the second piston 46 and the first cylinder hole 38. These pipelines are respectively connected to unillustrated compressors and the like. A center bladder 84 is disposed on radially outer surfaces of the center drum 12 and the side drum 14. Each end of the center bladder 84 is attached by being fitted in a groove provided in an axially outer wall surface of the square hole 40 in the slide base 32. The center bladder 84 is adapted to be inflated with air which is supplied by an air-supplying means. The center bladder 84, when not inflated, is kept in close contact with the outer peripheral surfaces of the center drum 12 and the side drum 14, as shown in Fig. 1. Here, in a state in which the slide bases 32 are spaced apart from each other, and the piston 62 and the first piston 44 (and the second piston 46) are spaced away most from the center drum 12, the diameters of the center drum 12 and the side drum 14 are reduced most and assume the same outside diameter (see Figs. 5 and 6). At the same time, this outside diameter becomes substantially the same as that of the slide base 32. Next, a description will be given of the procedure of forming a green tire of the up-down structure by using the tire-forming drum 10 of this embodiment in accordance with the following steps (1) to (6): (1) In the tire-forming drum 10 in an initial state shown in Fig. 1, a carcass ply 86 for up-ply use is mounted on the outer peripheries of the center bladder 84 and the side bladders 72, as shown in Fig. 2. It should be noted that the carcass ply 86 for up-ply use has such a width that each of its ends is located at a position spaced apart a predetermined dimension axially outwardly of the bead-placing portion 68. (2) After each annular bead core 88 is placed on that portion of the outer periphery of the carcass ply 86 for up-ply use that is located on the radially outer surface of the bead-placing portion 68, compressed air is filled in the air chamber 77 through the pipeline 79 to move the piston 62 in the axially inward direction (i.e., toward the center drum). Consequently, each roller 70 provided on the small slide block 66 rolls on the tapered surface 62A of the piston 62, thereby causing the slide block 66 to move radially outwardly, as shown in Fig. 2. As a result, each bead-placing portion 68 presses the bead core 88 from inside in the radial direction of the drive shaft 16 with the side bladder 72 and the carcass ply 86 for up-ply use placed therebetween, thereby fixing the bead core 88 at a predetermined position. Subsequently, each annular bead filler 90 having a substantially triangular cross section is attached to the fixed bead core 88 at a predetermined position thereof. (3) After the drive shaft 16 in the state shown in Fig. 2 is rotated as shown in Fig. 3, and the side drums 14 are thereby moved in axially inward directions (i.e., in mutually approaching directions) until they are made to abut against the center drum 12, compressed air is filled in the second air chamber 80. Both the second piston 46 and the first piston 44 connected thereto move in the axially inward direction, so that each slide block 52 connected to the first piston 44 by means of the link 54 moves in the radially outward direction. Hence, the diameter of each side drum 14 is enlarged until the outer peripheral surface of the center bladder 84 abuts against the inner peripheral surface of the carcass ply 86 for up-ply use, while the diameter of the center drum 12 abutting against the side drums 14 is also enlarged (see Fig. 3). Here, each side bladder 72 is inflated (as indicated by a phantom line in Fig. 3), and the inflated side bladder 72 is pressed in the axially inward direction by a push can 92 from the axially outer side, thereby causing an end portion of the carcass ply 86 for up-ply use to be turned up about the bead core 88. The turn-up portion is pressed by stitching rollers 96 substantially from the axially outward side so as to adhere to a main-body portion or the carcass ply 86 for up-ply use, the bead core 88, and the bead filler 90. Since the diameter of the bead-core fixing means constituted by the bead-placing portions 68 is enlarged along the radially outward direction of the drive shaft 16, and the bead cores 88 are thus fixed by the bead-placing portions 68, the positions of the bead cores 88 are not offset during the turning-up operation. In addition, since the side drums 14, whose diameters are enlarged until the outer peripheral surface of the center bladder 84 abuts against the inner peripheral surface of the carcass ply 86 for up-ply use, are disposed on the radially inner side of the carcass ply 86 for up-ply use, each turn-up portion can be reliably adhered to the main-body portion of the carcass ply 86 for up-ply use, the bead core 88, and the bead filler 90 by being pressed by the stitching rollers 96. (4) A carcass ply 94 for down-ply use is attached at a predetermined position on the outer periphery of the carcass ply 86 for up-ply use with both ends turned up, and the carcass ply 94 for down-ply use is pressed from above by the stitching rollers 96 so as to be adhered to the carcass ply 86 for up-ply use. Since the center drum 12 and the side drums 14, the diameters of which are enlarged until the outer peripheral surface of the center bladder 84 abuts against the inner peripheral surface of the carcass ply 86 for up-ply use, are disposed on the radially inner side of the carcass ply 94 for down-ply use, the carcass ply 94 for down-ply use can be reliably adhered to the carcass ply 86 for up-ply use by being pressed by the stitching rollers 96. (5) A side tread 98 is attached to the radially outer surface of the carcass ply 94 for down-ply use at a predetermined position thereof, and the side tread 98 is pressed from above by the stitching rollers 96 so as to be adhered to the carcass ply 94 for down-ply use. In this case as well, since the center drum 12 and the side drums 14, the diameters of which are enlarged until the outer peripheral surface of the center bladder 84 abuts against the inner peripheral surface of the carcass ply 86 for up-ply use, are disposed on the radially inner side of the side tread 98, the side tread 98 can be reliably adhered to the carcass ply 94 for down-ply use by being pressed by the stitching rollers 96. (6) As shown in Fig. 4, compressed air is supplied to the radially inner side of the center bladder 84 via unillustrated pipelines to inflate the center bladder 84. At the same time, the drive shaft 16 is rotated to move each slide base 32 further axially inwardly. At this juncture, the tapered surfaces 14E of each side drum 14 slide on the tapered surfaces 12E, 12F of the center drum 12. As a result, the side drums 14 push the center drum 12 radially outwardly and enters to the inner side of the center drum 12, causing the bead cores 88 to be moved axially inwardly. Consequently, the carcass ply 94 for down-ply use and the carcass ply 86 for up-ply use undergo enlargement of their diameters, and their configuration becomes close to that of the carcass of the product tire. Finally, additional component parts of the tire such as a belt 100 and a top tread 102 are attached at a predetermined position on the green case obtained as described above, thereby completing a green tire. In the tire-forming drum 10 in this embodiment, since the center drum 12 and the side drums 14, which are rigid members, are disposed on the reverse side of the carcass ply 86 for up-ply use, the carcass ply 94 for down-ply use can be reliably adhered to the carcass ply 86 for up-ply use by means of the stitching rollers 96. In addition, unlike the two-stage method, the formation of a green tire can be effected by a single tire-forming drum up to the completion of the tire by using the tire-forming drum 10 of this embodiment. Since the bead cores 88 are fixed and are prevented from moving undesirably, it is possible to efficiently manufacture green tires having excellent uniformity. Reference signs in the claims are intended for better understanding and shall not limit the scope.

Claims: A tire-forming drum (10) comprising: a center drum (12) divided into a plurality of segments (12A, 12B) in a circumferential direction and capable of expanding or contracting in a radial direction; a pair of side drums (14) respectively provided in juxtaposition to both axial sides of said center drum (12) and each divided into a plurality of segments (14A, 14B) in the circumferential direction, said pair of side drums (14) being capable of expanding or contracting in the radial direction and capable of being inserted into a radially inner side of said center drum (12); supporting means (22, 30) disposed coaxially with axes of said center drum (12) and said side drums (14) so as to support said center drum (12); urging means (28) or urging said plurality of segments of said center drum (12) in a direction in which a diameter of said center drum (12) is reduced in the radial direction; a pair of slide bases (32) for respectively supporting said pair of side drums (14) in such a manner that said side drums (14) are movable along an axial direction of said supporting means (22); side-drum-diameter enlarging means (44, 46, 50, 52, 54) provided for each of said slide bases (32) so as to enlarge and reduce a diameter of each of said side drums (14) in the radial direction by moving said segments of each of said side drums (14) in the radial direction; slide-base moving means (16, 18, 20, 36) for moving said slide bases (32) along the axial direction of said supporting means (22, 30); first tapered portions (14E) respectively provided at those ends of said plurality of segments constituting said side drum (14) that oppose said center drum (12); second tapered portions (12E, 12F) respectively provided at those ends of said plurality of segments constituting said center drum (12) that oppose each of said side drums (14), said second tapered portions (12E, 12F) corresponding to said first tapered portions (14E); a center bladder (84) formed in a hollow cylindrical shape in such a manner as to cover outer peripheral surfaces of said center drum (12) and said side drums (14) and to be inflatable radially outwardly of said center drum (12) from a state in which said center bladder (84) is adhered to the outer peripheral surfaces of said center drum (12) and said side drums (14), both axial sides of said center bladder being respectively supported by said slide bases (32); a pair of bead-core fixing means (62, 66, 70) respectively disposed on said slide bases (32) and located on respective axial sides of said center bladder (84) in such a manner as to be movable in the axial direction, said pair of bead-core fixing means (62, 66, 70) being capable of expanding or contracting for supporting a pair of bead cores (88) thereon in a radially outward direction of said bead-core fixing means (62, 66, 70), and further being adapted to be movable inwardly in said axial direction to a first predetermined position such that the distance between the pair of bead cores (88) is shortened to a first predetermined distance and further movable inwardly in said axial direction to a second predetermined position such that the distance between the pair of bead cores (88) is shortened to a second predetermined distance, said second predetermined distance being shorter than the first predetermined distance, and a pair of side bladders (72) respectively provided for said pair of slide bases (32) and capable of expanding or contracting in the radial direction for turning up those end portions of a ply (86) that project axially outwardly of the respective bead cores (88), from an axially outer side toward an axially inner side of said bead-core fixing means (62, 66, 70), said ply (86) being attached to an outer peripheral surface of said center bladder (84). A tire-forming drum according to Claim 1, wherein said supporting means (22, 30) has an elongated hollow cylindrical member (22) for supporting said center drum (12) at a predetermined axial position of said center drum (12). A tire-forming drum according to Claim 2, wherein said supporting means (22, 30) has supporting members (30) disposed on an outer peripheral surface of said hollow cylindrical member (22) so as to support said center drum (12) in such a manner as to allow said center drum (12) to be movable only in the radial direction. A tire-forming drum according to Claim 1, wherein said urging means (28) is disposed in said supporting means (22, 30). A tire-forming drum according to Claim 4, wherein said urging means (28) is constituted by coil springs. A tire-forming drum according to Claim 1, wherein said slide-base moving means (16, 18, 20, 36) has a drive shaft (16) for transmitting a rotatively driving force from an external driving source to said slide bases (32). A tire-forming drum according to Claim 6, wherein said drive shaft (16) has a right-handed thread (18) and a left-handed thread (20) which are juxtaposed in a longitudinal direction of said drive shaft (16). A tire-forming drum according to Claim 7, wherein said slide-base moving means (16, 18, 20, 36) has a pair of internally threaded members (36) coupled respectively to said slide bases (32), one of said pair of internally threaded members (36) meshing with the right-handed thread (18), another one of said pair of internally threaded members meshing with the left-handed thread (20). A tire-forming drum according to Claim 6, wherein said drive shaft (16) is disposed in such a manner as to be inserted into an elongated hollow cylindrical member (22) provided in said supporting means (22, 30). A tire-forming drum according to Claim 1, wherein each of said bead-core fixing means (62, 66, 70) has a plurality of first slide blocks (66) provided at predetermined intervals along a circumferential direction of said center bladder (84), each of said plurality of first slide blocks (66) being provided in such a manner as to be movable only along a radial direction of said center bladder (84) and having a roller (70) supported rotatably in a vicinity of a radially inner end of each of said plurality of first slide blocks (66). A tire-forming drum according to Claim 10, wherein each of said bead-core fixing means (62, 66, 70) includes a first piston (62) having a tapered surface (62A) capable of abutting against said rollers (70), said rollers (70) being adapted to move on the tapered surface (62A) as said first piston (62) moves. A tire-forming drum according to Claim 1, wherein said side-drum-diameter enlarging means (44, 46, 50, 52, 54) includes a plurality of second slide blocks (52) provided in correspondence with respective ones of said plurality of segments (14A, 14B) of said side drum (14), said plurality of second slide blocks (52) being provided movably only in a radial direction of said side drum (14). A tire-forming drum according to Claim 12, wherein said side-drum-diameter enlarging means (44, 46, 50, 52, 54) includes a second piston (44) for moving said plurality of second slide blocks (52) in the radial direction of said side drum as said second piston (44) moves in a direction parallel with an axial direction of said side drum (14). A method of manufacturing a green tire, comprising: providing a tire-forming drum (10) including: a center drum (12) divided into a plurality of segments (12A, 12B) in a circumferential direction and capable of expanding or contracting in a radial direction; a pair of side drums (14) respectively provided in juxtaposition to both axial sides of said center drum (12) and each divided into a plurality of segments (14A, 14B) in he circumferential direction, said pair of side drums (14) being capable of expanding or contracting in the radial direction and capable of being inserted into a radially inner side of said center drum (12); a center bladder (84) formed in a hollow cylindrical shape in such a manner as to cover outer peripheral surfaces of said center drum (12) and said side drums (14) and to be inflatable radially outwardly of said center drum (12) from a state in which said center bladder (84) is adhered to the outer peripheral surfaces of said center drum (12) and said side drums (14), both axial sides of said center bladder (84) being respectively supported by a pair of slide bases (32) for supporting said pair of side drums (14); a pair of bead-core fixing means (62, 66, 70) respectively disposed on said slide bases (32) and located on respective axial sides of said center bladder (84) in such a manner as to be movable in an axial direction, said pair of bead-core fixing means (62, 66, 70) being capable of expanding or contracting for supporting a pair of annular bead cores (88) thereon in a radially outward direction of said bead-core fixing means (62, 66, 70); and a pair of side bladders (72) capable of expanding or contracting in the radial direction for turning up those end portions of a ply (86) that project axially outwardly of the respective bead cores (88), from an axially outer side toward and axially inner side of said bead-core fixing means (62, 66, 70), said ply (86) being attached to an outer peripheral surface of said center bladder (84); a first step of positioning said side drums (14) in juxtaposition to the respective axial sides of said center drum (12), setting outside diameters of said center drum (12) and said side drums (14) to a substantially identical outside diameter, and attaching a first carcass ply (86) serving as an up-ply to an outer periphery of said center bladder (84) kept in close contact with outer peripheral surfaces of said center drum (12) and said side drums (14), such that each axial end of the first carcass ply (86) is located at a position spaced a predetermined distance apart axially outwardly of said bead-core fixing means (62, 66, 70); a second step of placing each of the bead cores (88) over a radially outer surface of each of said bead-core fixing means (62, 66, 70) via the first carcass ply (86) attached to said center bladder (84), and enlarging a diameter of each of said bead-core fixing means (62, 66, 70) as so to fix each of the bead cores (88) together with the first carcass ply (86) in the radially outward direction of said bead-core fixing means (62, 66, 70); a third step of attaching each of a pair of bead fillers (90) to each of the fixed bead cores (88) at a predetermined position thereof; a fourth step of moving said pair of bead core fixing means (62, 66, 70) inwardly in said axial direction such that the distance between the pair of bead cores (88) is shortened to a first predetermined distance; a fifth step of enlarging the diameters of said side drums (14) and said center drum (12) until the outer peripheral surfaces of said side drums (14) and said center drum (12) abut against an inner peripheral surface of the first carcass ply (86); a sixth step of turning up in an axially inward direction of said bead-core fixing means (62, 66, 70) each axial end portion of the first carcass ply (86) about the bead core (88) with the bead filler (90) attached thereto by inflating each of said side bladders (72), so as to cause each turn-up portion of the first carcass ply (86) to be pressed against and adhered to a main-body portion of the first carcass ply (86), the bead core (88), and the bead filler (90); a seventh step of attaching a second carcass ply (94) serving as a down-ply to the first carcass ply (86) whose end portions are turned up, so as to cause the entire second carcass ply (94) to be pressed against and adhered to the first carcass ply (86) whose end portions are turned up; an eighth step of attaching a pair of side treads (98) at predetermined positions on an outer peripheral surface of the second carcass ply (94) adhered to the first carcass ply (86); a ninth step of inflating said center bladder (84) so as to inflate the first carcass ply (86) and the second carcass ply (94) which are superposed on said center bladder (84), moving said side drums (14) and said pair of bead core fixing means (62, 66, 70) in respectively axially inward directions such that the distance between the pair of bead cores (88) is shortened to a second predetermined distance, said second predetermined distance being shorter than the first predetermined distance, and expanding or contracting at least one of said center drum (12) and said side drums (14), and inserting said side drums (14) to the radially inner side of said center drum (12), so as to allow the bead cores (88) to approach each other; and a tenth step of attaching a belt (100) and a top tread (102) at a predetermined position on the inflated second carcass ply (94) superposed on the inflated first carcass ply (86). A method of manufacturing a green tire according to Claim 14, wherein, in the second step, the diameter of each of said bead-core fixing means (62, 66, 70) is enlarged such that a radially outer surface of each of said bead-core fixing means (62, 66, 70) is located radially outwardly of radially outer surfaces of said center drum (12) and said side drums (14). A method of manufacturing a green tire according to Claim 15, wherein each of said bead-core fixing means (62, 66, 70) has a plurality of first slide blocks (66) provided at predetermined intervals along a circumferential direction of said center bladder (84), each of said plurality of first slide blocks (66) being provided in such a manner as to be movable only along a radial direction of said center bladder (84) and having a roller (70) supported rotatably in a vicinity of a radially inner end of each of said plurality of first slide blocks (66), and wherein, in the second step, distal ends of said plurality of first slide blocks (66) fix each of the bead cores (88) as said plurality of first slide blocks (66) move in the radially outward direction. A method of manufacturing a green tire according to Claim 16, wherein each of said bead-core fixing means (62, 66, 70) includes a first piston (62) having a tapered surface (62A) capable of abutting against said rollers (70), and wherein, in the second step, said plurality of first slide blocks (66) move in the radially outward direction as each of said rollers (70) moves on the tapered surface (62A) in conjunction with the movement of said first piston (62). A method of manufacturing a green tire according to Claim 14, wherein the enlargement of the diameters of said side drums (14) and said center drum (12) in the fifth step is effected by causing axially opposing ends of said side drums (14) to abut against corresponding axial ends of said center drum (12) and by moving said side drums (14) in the radially outward direction. A method of manufacturing a green tire according to Claim 18, wherein, in the fifth step, the diameters of said side drums (14) and said center drum (12) are enlarged such that radially outer surfaces of said center drum (12) and said side drums (14) are located radially outwardly of a radially outer surface of each of said bead-core fixing means (62, 66, 70). A method of manufacturing a green tire according to Claim 18, wherein said side drums (14) and said center drum (12) have tapered surfaces (12E, 12F, 14E), respectively, and the tapered surfaces (14E) of said side drums (14) and the tapered surfaces (12E, 12F) of said center drum (12) are provided in such a manner as to be capable of abutting against each other and to be slidable with respect to each other, and wherein the approaching of the bead cores (88) toward each other in the ninth step is effected as the tapered surfaces (14E) of said side drums (14) and the tapered surfaces (12E, 12F) of said center drum (12) are made to abut against each other and are slid with respect to each other such that said side drums (14) move in mutually approaching directions.

Inventors: KUMAGAI YUZO, MATSUYAMA FUMIHIRO, KUMAGAI, YUZO, MATSUYAMA, FUMIHIRO
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1994
Main classification: B29D30
IPC codes: B29D30, B32B27, B41N1